A large number of patients with both neoplastic and non-neoplastic inappropriate secretion of thyrotropin have been investigated. Fibroblasts from patients with generalized thyroid hormone resistance display abnormal kinetics of triiodothyronine nuclear uptake. Thyroid hormone and thyrotropin-releasing hormone regulate the bioactivity of thyrotropin. The carbohydrate of thyrotropin is not essential for receptor binding but is necessary for receptor coupling to adenylate cyclase.